Stray voltage is a difference in electrical potential or a voltage that exists outside of an electrical delivery system. One form of stray voltage is neutral-to-earth (“NE”) voltage. NE voltage is an electrical potential or voltage between the neutral of an electrical delivery system and an earth ground. NE voltages may be created as a consequence of the architecture of an electric power distribution system. In general, electric power is distributed from a generation site to a number of substations. In one relatively common distribution path, high voltage electricity from a substation is delivered to a line transformer located at a facility that consumes electricity, such as a home, business, or farm. As the distance from the line transformer to the substation increases, an electrical potential between the primary neutral of the line transformer and earth ground increases. The National Electrical Safety Code (“NESC”) specifies that utilities connect the neutral on the primary side of a facility's step down transformer to the neutral on the secondary side of the transformer. The purpose of this is to prevent excessively dangerous voltage levels in the event of an open circuit on the primary neutral. However, this recommended connection can cause a situation where the difference in potential of the primary neutral to earth ground is passed to the secondary neutral. The difference in potential can reach a relatively significant level, such as twenty volts.
Another form of stray voltage is an electrical potential that exists between two points susceptible to contact simultaneously by an animal. For example, some electrical distribution systems are designed to utilize the earth as a return path for current to the substation. More specifically, the earth is used as a current return in parallel to the primary neutral. Differences in the impedance of soils may result in differences in electrical potential between two points of earth ground or the earth ground and the electrical system neutral. Thus, it is possible that an animal may simultaneously contact points that have different potentials resulting in current traveling through the animal's body.
The Public Service Commission of Wisconsin has developed a protocol for determining if stray voltage exists on a facility such as a dairy farm. The protocol includes four main tests:                Primary neutral to a remote ground rod voltage        Main service panel neutral to a remote ground rod voltage        Voltage drop in the neutral wire between the primary transformer and the main service panel        Cow contact voltage (obtained by measuring the voltage drop across a 500 ohm resistor shunted between two potential contact points, e.g., a drinking cup and a barn floor)        
The tests are conducted for 24 to 48 hours and the results analyzed to determine if stray voltage, or the potential for stray voltage, exists at the facility.